Log Entries in Service Portal Log created by Guest user



Why there are Service Portal Log entries created by "Guest" user?


When the customer logins, the transaction runs as a guest user as it has not authenticated a user yet, so the transaction will show as guest. 
With that transaction, it will authenticate the user and then the session will be considered as the user_ID, if the login fails then it will redirect to the logout screen. 

To verify that you can perhaps try to login the portal, go to transaction log to find the session ID for this particular user and then in the system log, you can trace down and see the first transactions are actually showing as guest but then it authenticates and shows the exact user account.